build: ignore PREFER_DEFINED_ATTRIBUTE_MACRO

The library doesn't defined attribute macros, thus no point in warning.
Furthermore, such macros should also not be used in the public interfaces
as it will pollute the namespace.

Signed-off-by: Daniel Wagner <[email protected]>

Author: igaw

.checkpatch.conf

@@ -22,3 +22,6 @@
 
 # Avoid "Does not appear to be a unified-diff format patch" message
 --ignore NOT_UNIFIED_DIFF
+
+# Do not warn for __attribute__((XXX)) is used
+--ignore PREFER_DEFINED_ATTRIBUTE_MACRO